New strategy of platelet substitutes for enhancing platelet aggregation at high shear rates: Cooperative effects of a mixed system of fibrinogen γ-chain dodecapeptide- or glycoprotein Ibα-conjugated latex beads under flow conditions

To construct platelet substitutes that have hemostatic properties over a wide range of shear rates, we used fibrinogen γ-chain carboxy-terminal sequence HHLGGAKQAGDV (H12), which recognizes activated platelets at low shear rates, and a recombinant water-soluble moiety of the platelet glycoprotein (rGPIbα), which recognizes von Willebrand factor at high shear rates. Three kinds of samples were prepared for this purpose: H12-conjugated latex beads (H12-latex beads), rGPIbα-latex beads, and H12/rGPIbα-latex beads. These samples were evaluated in thrombocytopenia-imitation blood at various flow conditions. Based on ADP-induced platelet aggregation studies, the H12-latex beads significantly enhanced platelet aggregation via H12 binding with GPIIb/IIIa activated on the surface of activated platelets, whereas the rGPIbα-latex beads did not support platelet aggregation. In the case of the H12/rGPIbα-latex beads, the function of H12 was suppressed by steric hindrance from the larger rGPIbα bound to the latex bead. A mixture of the H12-latex beads and the rGPIbα-latex beads adhered to a collagen surface over a wide range of shear rates. In particular, at high shear rates, a cooperative effect was observed in the enhancement of platelet thrombus formation compared with H12-latex beads or rGPIbα-latex beads alone. We propose that a mixed system of H12- and rGPIbα-conjugated nanoparticles is a more effective platelet substitute than each of the beads used alone and has enhanced platelet aggregation properties.